An issue was discovered in the ProofreadPage extension for MediaWiki before 1.35.12, 1.36.x through 1.39.x before 1.39.5, and 1.40.x before 1.40.1. XSS can occur via formatNumNoSeparators.
https://phabricator.wikimedia.org/T345693
https://gerrit.wikimedia.org/r/c/mediawiki/extensions/ProofreadPage/+/961262